The present invention relates to an electromagnetic wave absorber having good electromagnetic wave absorbing characteristic and a high-frequency circuit package that uses the same.
A high-frequency circuit package is usually sealed hermetically by attaching a package lid made of a metallic or ceramic material having rectangular parallelepiped shape onto a package base. Consequently, as a cavity of rectangular parallelepiped shape is formed in the high-frequency circuit package, the high-frequency circuit package has a nature similar to that of a rectangular cavity resonator. As a result, cavity resonance occurs in the high-frequency circuit package in a frequency region higher than a shut-off frequency that is determined by the dimensions of the cavity. Therefore, when a high-frequency semiconductor device or other circuit element that operates in this frequency region is mounted in the high-frequency circuit package, the cavity becomes small enough to make the shut-off frequency sufficiently higher than the frequency region in which the device operates.
With this method, however, there has been such a problem that the resonance frequency of the cavity becomes lower than the frequency region in which the device operates, as the operating frequency of the device becomes higher. Recently, to counter this problem, such a method has been employed that suppresses the cavity resonance by providing an electromagnetic wave absorber in the high-frequency circuit package thereby absorbing the energy of electric field or magnetic field generated by the cavity resonance.
The electromagnetic wave absorbers known to be used in the high-frequency circuit package contain an electromagnetic wave absorber 72 comprising a ferrite sheet having rectangular parallelepiped shape that is attached to the back surface of a package lid 71 of a high-frequency circuit package 70 shown in FIG. 11, and one that is coated with a ferrite coating material (Japanese Unexamined Patent Publication (Kokai) No. 6-236935).
However, the ferrite sheet attached to the inside of the high-frequency circuit package 70 and the ferrite coating material must contain at least 20% by weight of a synthetic resin, which leads to lower fire resistance. A common practice to solve this problem is to add a fire retardant such as decabromodiphenyl oxide, TBA epoxy oligomer-polymer or TBA carbonate oligomer, thereby to improve the fire resistance. However, these fire retardants are compounds containing Br and/or Cl, and evolve a gas containing Br and/or Cl when heated.
In case the electromagnetic wave absorber 72 containing such a fire retardant is attached to the inside of the high-frequency circuit package 70, heat generated when soldering the package lid 71 to the package base 73 or soldering the high-frequency circuit package 70 to a mother board (not shown) causes the evolution of a gas containing Br and/or Cl that fills the inside of the high-frequency circuit package 70. Since such a gas is corrosive in nature, the gas causes corrosion of a semiconductor device (not shown) mounted in the high-frequency circuit package 70 and a transmission line (not shown) that is formed on the package base 73.
Evolution of the gas may be avoided by using a functional ceramic material such as Ni ferrite, Nixe2x80x94Zn ferrite or Mnxe2x80x94Zn ferrite for the electromagnetic wave absorber. However, such ferrite materials can be usually used only for an electromagnetic wave absorber intended for frequencies of several mega hertz. There have been demands for an electromagnetic wave absorber that can be used in high-frequency region of 10 GHz and higher, but desired electromagnetic wave absorbing characteristic cannot be achieved even with the electromagnetic wave absorber that can be used in high-frequency region of 10 GHz and higher.
A major object of the present invention is to provide an electromagnetic wave absorber that has good electromagnetic wave absorbing characteristic and does not generate a corrosive gas, and a high-frequency circuit package that uses the same.
Another object of the present invention is to provide an electromagnetic wave absorber that is used mainly as a component part of a high-frequency circuit package operating in a high-frequency region of 10 GHz and higher, and the high-frequency circuit package that uses the same.
Still another object of the present invention is to provide an electromagnetic wave absorber that can be easily manufactured and a high-frequency circuit package that uses the same.
In order to achieve the objects described above, the electromagnetic wave absorber of the present invention comprises a sintered body that contains Fe and at least one element selected from the group consisting of Si, Mg, Zr, Ni, Al and Co, wherein attenuation of electromagnetic wave of said sintered body is less than 2 dB at frequencies of 10 GHz or higher.
(1) The sintered body that contains Fe and at least one element selected from Si, Mg and Zr contains 20 to 95 mol % of Fe on Fe2O3 basis, and 5 to 80 mol % in total of at least one element selected from Si, Mg and Zr on SiO2, MgO and/or ZrO2 basis. The sintered body may also contain 1 to 50 mol % of Al on Al2O3 basis. The Fe content is more preferably in a range from 40 to 90 mol % on Fe2O3basis.
(2) The sintered body that contains Fe and Ni is made of Fe2O3 as the main component and NiO in the remainder. The Fe2O3 content is preferably in a range from 70 to 95 mol %, with the remainder containing NiO. The remainder also preferably contains at least one selected from ZnO, CuO and Bi2O3.
(3) The sintered body that contains Fe and Al is made of Fe2O3 and Al2O3, of which content being 20 mol % or more for Fe2O3 and 80 mol % or less for Al2O3. The content of Fe2O3 is preferably in a range from 40 to 90 mol %. Besides Fe2O3 and Al2O3, the remainder contains at least one selected from ZnO, CuO and Bi2O3.
(4) The sintered body that contains Fe and Co is made of Fe2O3 and CoO, of which content being 45 mol % or more for Fe2O3 and 55 mol % or less for CoO. The content of Fe2O3 is preferably in a range from 55 to 90 mol %. Besides Fe2O3 and CoO, the remainder contains at least one selected from ZnO, MnO, NiO, CuO and Bi2O3.
(5) The electromagnetic wave absorber of the present invention has volume resistivity of preferably 5xc3x97105 xcexa9xc2x7m or lower.
A first high-frequency circuit package according to the present invention comprises a package base and a package lid attached to the package base, with the electromagnetic wave absorber described above installed therein.
A second high-frequency circuit package according to the present invention comprises a package base and a package lid attached to the package base, with the package lid being formed from the electromagnetic wave absorber described above.
Objects and advantages of the present invention will become apparent as one reads the detailed described that follows.